Nearly half of all Tampa Bay homes with a mortgage were underwater at the end of 2009. First American CoreLogic said negative equity afflicted 48.5 percent of residential mortgages. That's 332,968 homes. The rate continues to rise. About 46 percent of Tampa Bay homes were underwater at the end of September. Florida's upside-down mortgage rate was 47.8 percent, third worst in the nation after Nevada's and Arizona's. About 2.2 million of the state's 4.6 million residential mortgages were sucking seawater. A mortgage is underwater when a home owner owes more on his loan than the home is worth. Tampa Bay home depreciation exceeds 40 percent since 2006. The problem abets foreclosures: If a homeowner holds no equity he's less likely to make house payments.